Control signal generator



Match 22, 1960 Filed May 20, 1957 4 Sheets-Sheet 1 1/51 flu? 15 17 18 1 7 5/64/44 mzmm mm mm J mm MASTER WATEQ FZ'ED M fl ATTORNEYS- March 22, 1960 s. w. DANIEL CONTROL SIGNAL GENERATOR 4 Sheets-Sheet 2 Filed May 20, 1957 March 22, 1960 s. w. DAN| EL 2 ,929,878

CONTROL SIGNAL GENERATOR 4 Sheets-Sheet :5

Filed May 20, 1957 16 coMPmmr/w AMPUF/ER SIGNAL AMPt/F/ER II i M62 1? COMPEMWTYM SIGIVHL AM PL lF/ER J5}16 C OMPEAGHT/ON n AMPLIFIER.

SIGN/1L AMPLIFIER, Q mizgg AMPLIFIER S/GIVHL Srsn/qe'r 14 044054 United States Patent F signor to Milltronics Limited, Toronto, Ontario, Canada Application May 20, 1957, Serial No. 660,376 Claims priority, application Canada September 26, 1956 Claims. (Ci. 179-1) This invention relates to the sonic control of material reduction mills and like machines wherein sound emitted during the operation thereof varies with a condition of operation. More particularly, the invention relates to a method and means whereby an electrical signal which varies in accordance with the energy level of sound from a desired source may be produced notwithstanding the presence of extraneous sound produced from other sources within the same frequency ranges as the sound in accordance with which the electrical signal is to vary.

While the invention may be applied to the sonic control of any type of machine where sonic control is applicable, its nature and operation will be described in relation to the sonic control of material redu'ction* mills wherein the differentiation of direct grinding sound from extraneous sound has previously constituted a serious problem. H

In the past, attempts have been made to deal with this problem by restricting the frequency band to which the signal to be generated has been responsive, and sound shielding and directional microphones have been usedin an attempt to alternate as much as possible the extraneous sounds reaching the microphone. Whilesu ch steps are substantially reductive of the effect of extraneous sound, there are certain sound paths available to extraneous sound which cannot effectively be shielded, and certain extraneous sounds which fall within the restricted frequency ranges to which thesyste'm has been made responsive. Consequently, although the improvement brought about by such prior proposals has been marked, it has not completely done away with the adverse effect of extraneous sound, and in multiple mill installations, no previous method has been proposed which is capable of differentiating between the direct grinding noise of a mill being controlled, and extraneous grinding and other noises associated with the operation of adjacent mills and other operating machinery and other sources of noisesuch as whistles, klaxons, horns, shouts and etc.

According to the invention, a signal isgenerated which is responsive largely to the noise produced upon which' the control is to be based, and a second signal is generated which is responsive largely to the extraneous noise. These two signals are then combined in such away that the resultant signal is responsive to the noise produced upon which control is to be based. V 7

Apparatus according to the inventionsuitably consists of a first microphone, a compensatingmicrophone, each of the microphones being suitably equipped with sensitivity adjusting means and such directional,sound shielding, band pass filter or sensitivity means as maybe expedient, and means such as a bridge circuit or electronic tube network for combiningthe output signals from the microphone circuits in such a manner that the output signal is responsive to the difference between the outputs of the' two microphone circuits. I

In operation, the first microphone: will be positioned in the most favourable position to pick up the sound which it is desired to use' for control purposes. The com- 2 pensating microphone will be so positioned as to pick up more extraneous sound than control sound. The correct balance of the signals from each microphone will then be determined experimentally as is hereinafter described, and the signal which results from the comparison of the two signals in an amplifier is responsive only to the desired sound.

The invention will be further described with reference to the accompanying drawings, in which: I V Figure 1 is a diagrammatic representation of an installation of three grinding mills to illustrate the difli culties encountered when using acoustictype of control; Figur'eZ is a block diagram illustrating control apparatus in accordance with the invention;

.Figure 3 is a schematic diagram of electric circuits required for the apparatus illustrated in Figure 2 I Figure 4 is a schematic diagram illustrating a modification of Figure 3;

Figures 5 to 9 show block diagrams illustrating variations of control apparatus in accordance with the in} vention. e

A three mill installation for the grinding of ore is illustrated diagrammatically by Figure 1. The three mills, mill No. 1, mill No. Zand rnill No. 3, are arranged in side by side relationship. Each mill has a conventional ore feed arrangement 10, and mill No. 1 is shown provided with conventional water feed means 11. The three mills are supported in the ordinary manner from a foundationfioor 12 and each mill is provided with a microphone M1, M2 or M3 arranged to pick up grinding noise from within each mill.

As indicated in the opening paragraphs of this specification, it is desired to use the grinding noises reaching a microphone such as the microphone M1 for the mill No; 1, to control the rate of feed to the mill. However, the audible frequencies reaching the microphone M1 are complex sounds and broadly speaking are made up' of ambient vibrations, the desired grinding sounds from within mill No. 1, and undesired grinding sounds originating in the adjacent mills No. 2 and No. 3. The ambient sounds consist of all the sounds remaining when the mills are empty, that is, when no grinding work is being accomplished by the mill. In general, ambient sounds are, generated by motors, gear units, conveying systems; and other similar machinery. The frequencies involved in the, ambient sounds are in the range lower than 2000 to 2500 cycles per second. The higher energy levels are usually located at the low frequency end of the range, and above 1,000 cycles per second the energy levels are low. ,The desired grindingsounds originating in the mill No. 1, of which the feed is being controlled by'an electronic control system, have a frequency band roughly from 500 to over 6,000 cycles per second. Grinding sounds are measurable to higher than 60,000 cycles per second but the higher frequency sounds are of low magnitude. Grinding sound amplitudes are usually highest in the 1500 to 4,000 cycles per second range of' the auaig ble frequency band. The undesired grinding sounds originating in the adjacent mills No. 2 and No; 3 have the same characteristics as the desired sounds originating in the mill No. 1. It is apparent from this discussion that the microphone M1 by itself, cannot differentiate between undesired grinding sounds, ambient sounds, and desired grinding sounds. Also, it is difiicult if not impossible to shield acoustically the microphone Ml fro'rrf all sources of ambient sounds, for example, the sound paths indicated by the dashed lines DD, EE, and FF.

As will be apparent from the discussion to follow it is essential according to the present invention that the sounds to which the microphone M1 responds be for themost partmade up of direct-noise from within the mill No. 1. If this is not the case in a mill installation then steps must be taken to bring about this condition. For example, sound barriers such as barriers YY and ZZ of sound absorbing material can be erected to shield the mill No. 1 and its microphone M1 from the adjacent mills. These barriers can be made effective to attenuate the undesired sounds reaching the mill No. 1 to a great enough degree that for the most part the sounds reaching the microphone are grinding sounds from within the mill No. 1. For such an installation a change in magnitude of the sounds originating, for example, from mill N0. 2 produces a change in the signal being amplified by an amplifier connected to the microphone M1. According to the invention a similar amplifier connected to the microphone M2 is arranged to have an equal and opposite effect so that by combining the outputs of the two amplifiers into a common output a control signal voltage is obtained which is free of the eifect of the varying grinding sounds produced in the mill No. 2. Additional microphones may be fed into the compensating amplifier, for example, the microphones M2 and M3 may both feed the compensating amplifier. The microphones M2 and MS may be located in any positions found to furnish best compensation for the undesired grinding sounds from the mills with which they are associated. If required, additional microphones may be used to feed the compensating amplifier.

' Figure 2 shows a block diagram of an installation having two adjacent mills, mill No. 1 and mill No. 2. Mill No. 1 is the controlledmill and has its ore feed mechanism and its water feed means 11 controlled by signals produced from electronic circuits which are shown in block form. A signal microphone vMS1 is arranged to pick up desired grinding sounds from within the mill No. 1 but which, as explained in connection with Figure 1, will include undesired sounds such as those originating from within the adjacent mill No. 2. A compensation microphone MC2 is arranged to pick up the undesired sounds from within the mill No. 2.

The signal microphone M81 and the compensation microphone MC2 feed a signal amplifier 15 and a compensation amplifier 16 respectively. The amplified signals from the amplifiers 15 and 16 are each .fed to the inputs of an integration amplifier 17 and its output forms one of the inputs of an error signal amplifier 18. The other input of the error signal 18 is from a master system control 19. The error signal amplifier 18 provides two output signals, one to control the ore feed changing device 19, and the other to control the water feed changing device 20. The ore feed changing device 19 and the water feed changing device 20 are connected to the ore feed mechanism 10 and the water feed 11 respectively of the mill No. 1. With this arrangement and after the required operating conditions are set by adjustment of the master system control 19', the control of feed of both ore and water to the mill No. 1 is controlled automatically by the grinding sounds from within the mill No. 1, so that the most eflicient rate of grinding can be maintained.

Figure 3 shows schematically the circuits of the electronic equipment required for the installation shown in block form in Figure 2. The signal amplifier which comprises the tubes V1 and V3 and the compensation amplifier which comprises the tubes V2 and V4 have dentical circuits between their respective microphone inputs M81 and M82 up to and including capacitors C5 and C6. The sound vibrations reaching the'microphone M S1 are converted by the microphone MS1 into electncal signals. The impedance matching transformer T1 and the tube VIA amplify these electrical signals. The resonant circuit L1C1 is a band pass filter to pass for example frequencies around 3,300 cycles per second to the grid of the tube VIB. The tube VIB amplifies the pass band frequencies. The voltage doubler tube WA and WE converts the amplified electrical s gn l M 4 to a direct current voltage across a capacitor C7. The positive voltage across the capacitor C7 (the voltage between the points C and A) is proportional to the magnitude of the pass band sound vibrations reaching the signal microphone MS1.

In a similar manner to that just described, the tubes V2A, V2B, V4A and V4B of the compensation amplifier convert the sounds reaching the compensation microphone MC2 into a unidirectional voltage across capacitor C8. The tube V4 is inverted with respect to the connections of the tube V3 to produce a negative signal across the capacitor C8.

The capacitors C7, C8 and the resistors R7, R8 are connected to form a direct current bridge network. The output of the bridge appears as a voltage between the points C and D and, assuming that theresistors R7 and R8 have the values 200K and 510K ohms respectively,

Volts C-D The values of resistors R7 and R8 were chosen on the assumption that the ratio of-- Desired grinding sound amplitudes (M81) Undesired grinding sound amplitudes (MC2) will always be greater than 510/200; i.e. the signal/noise ratio will be equal to, or greater than, 2.5/ l. a This can be proved as follows:

(a) Assumemills Nos. 1 and 2 shut down. Controls P1 and P2 are turnedoif. I I I y (b) Statt up mill No. I, adjust P1 for a CA voltage of say 69.6 volts. Voltage CD will be (.718X69.6) (.28 10)=50 volts.

(0) Start up mill No. 2. AssumeCA increases to 89.6 volts; CD increases to 64.3 volts. Adjust P2 until voltage CD is again 50 volts.

(d) Voltage CB will be 51.1 volts. This is the amount of compensation required.

(e) With mills Nos 1 and 2 grinding: voltage CD |=(.718 69.6)(.28 51.1)=50 volts.

(f) with Mill No. l grinding, mill No. 2 stopped; voltage CD=(.718 69'.6)-(.28 0)=50 volts.

In actual practice the above mathematics are not used. It is merely necessary to adjust P1 for the desired voltmeter reading (say 50 volts), with the con trolled mill running and all other mills stopped. The adjacent or neighboring mills are started up, and the voltmeter reading is readjusted to the same 50 volts by means of P2.

During normal operations the magnitude of the grinding sound is, rapidly fluctuating in characteristic recurrent sound peaks or spikes. It is desired to average these fluctuations into a reasonably steady signal. The integration control, P3, and capacitors C9, C10, form a long time constant-low pass filter, for example:

(a) By selecting the setting of P3 and using C9, C10 in series, singly, or in parallel, time constants of 2.5 to 20 seconds may be obtained. If necessary additional capacitors may be connected in parallel with C9, C10.

.(b) When the plate of tube VSA is not connected to C9, the charge and discharge time constants are nearly equal.

(0) The vibration signals from some mills, notably rod mills, are characterized by steep wave front, sharp peaked, sound spikes.

(d) On any mill, a sharp decrease in the average sound level indicates an approaching mill overload condition. It is advisable to rapidly decrease the ore feed to the C nversely it is not desirab e to suddenly inhhhasrs The tube VSB is used as an impedance matching device to convert the high resistance between the points CF into a low impedance, suitable for the output signals.

The resistance network R10, R11, is used to furnish a bias voltage to the grid of tube VSB. This bias voltage ensures that the output voltmeter will read zero volts for zero sound.

The following is an example of component values for a typical design of the circuit shown in Figure 3:

M81 Signal microphone, for desired grinding sounds. MCZ Compensation microphone, for undesired grinding sounds.

R1, R 2, R5 and R6 1,000 ohm. 1 watt resistors.

R3 and R4 51,000 ohm, 1 watt resistors.

R7 200.000 ohm. 1 watt resistor.

R8 and R9 1. 510.000 ohm, 1 watt resistors. "5.000 ohm. 1 watt resistor.

100.000 ohm. 1 watt resistor. 31'500 mmfd. capacitors in parallel. 1500 mmfd. capacitors.

.05 mfd. capacitors.

.1 mfd capacitors.

10.0 mfd, capacitors.

- 50.000 ohm potentiometers.

500.000 ohm potentiometer.

' Microphone transformers. L1 and L2 Variableinductors-nominally 500 11111.

L3 and L4 Reactors 60 H. V1, V2 and V5 Tytplsi)12)AT7 tubes (alternatives 12AU7 e V3 and V4 Type 6AL5 tubes (alternatives 6H6 tubes).

Figure 4 shows a modification of the circuit shown in Figure 3 in which three compensation microphones MCZ, MC3 and MC4 are used in place of the singlecompensation microphone M02 shown in Figure 3. The signals from the three microphones are combined into acommon signal fed to the transformer T2 by a series connection of three potentiometers P5, P6 and P7 which are individually connected across the outputs of the microphones MC2, MC3 and MC4. The required relative amplitudes of signals from the three microphones can be set by adjustment of the potenticmeters P5, Pr? and P7 to provide a combined compensating signal at the transformer P2 as required to provide proper compensation for the signal from the signal amplifier.

Figures 5 to 8 show variations of'the arrangement of the control apparatus for an installation having two adjacent mills such as the mills Nos. 1 and 2. In Figure 5 the mill No. l is controlled and its signal microphone M81 is fed to the signal amplifier 15. 1A compensation microphone MCI is arranged above themill No. 2 to pick up the undesired grinding noises from it and to feed them to the compensation amplifier 16. The signal amplifier '15 and the compensation amplifier '16 are the same amplifiers as shown in the block diagram of Figure 2, and these amplifiers in turn feed into the remainder of the apparatus as shown in Figure 2.

Figure 6 shows a case in which both the adjacent mills Nos. 1 and 2 are controlled in accordance with the invention and each mill has its respective signal microphone M81 and M82. The signal microphone M81 feeds into a signal amplifier 15' and the signal microphone M82 feeds into a signal amplifier 15'. The compensation microphone MC which feeds the compensation aniplifier 16' of the control system for the No. 1 mill is located above the mill No. 2 to pick up grinding sounds from it. The compensation microphone MCZ which feeds the compensation amplifier 16" of the control system No. 2 for the mill No. 2 is located above the mill 1 to pick up the grinding sounds from it. With this arrangement both mills can be controlled in accordance with the invention, and in the case of each mill compensation is provided for the sounds reaching it from the adjacent mill. The remainder of each of the control systems Nos. 1 and 2 is the same as that illustrated in Figure 2.

Figure 7 shows the control system in accordance with the invention applied to two adjacent mills and using a single compensation microphone MC1/MC2. The compensation MCI/M02 feeds to both the compensation amplifiers 16' and 16". The remainder of the system is the same as that described with reference to Figure 6. The compensation microphone MC1/MC2 is located to pick up grinding sounds from both of the mills Nos. 1 and 2 so that the composite signal from the microphone can be used to compensate for undesired grinding sounds picked up by each of the signal microphones M81 and M82.

Figure 8 shows an arrangement of the control apparatus in accordance with the invention, in which for each mill a single microphone is used as both the signal microphone and the compensation microphone. The microphone MCl/MCZ is located at the mill No. 1 and it provides a signal to the signal amplifier 15' as well as to the compensation amplifier 16". Similarly, the microphone MS2/MC1 is located at the mill No. 2 and feeds a signal to the signal amplifier 15" and to the compensation amplifier 16'. The remainder of the control systems for each of the mills Nos. 1 and 2 is the same as that shown in Figure 2.

Figure 9 shows control apparatus in accordance with the invention arranged to control each of four adjacent mills Nos. 1, 2, 3 and 4. A signal microphone M81, M52, M83, M84 is arranged at each of the mills and each signal microphone feeds a signal to its corresponding signal amplifier 15', 15", 15" and 15" of each of the control systems Nos. 1, 2, 3 and 4 connecting to control the feed to the mills Nos. 1, 2, 3 and 4 in a similar manner to that shown in Figure 2. As indicated in Figure 9 by the squares C there are many possible locations for each of the compensation microphones MCI, MCZ MC3 and MC4. The compensation microphones feed their respective compensation amplifiers 167, 16'', 16 and'16"". I

Figures 5 to 9 indicate some of the many installations which can be designed in accordance with the invention. A fundamental consideration is to locate the signal microphone at the point of maximum ratio of signal to interference wherever this may be. Similarly the interference compensation microphone should be located at the point of maximum ratio of interference to signal wherever this may be. It may be necessary in some installations to try several locations to findthe best locations for the signal and compensation microphones. The higher the signal interference ratio from the signal microphone and the higher the interference signal ratio from the compensation microphone the easier the adjustment of the apparatus, and the more effective the compensation obtained. The compenation microphones may be wide angle and/or directional types. If necessary, two or more microphones may be used to compensate one amplifier. Also one cornpensation microphone may be used to compensate two or more amplifiers. In most cases it will be preferable to have a directional type microphone for the signal microphone.

What I claim as my invention is:

1. Apparatus for producing an electrical control signal which varies in accordance with the sound produced by a desired first source, comprising; two spatially separated sources of sound the first a desired source and the second an undesired source a first microphone positioned adjacent the first source and adapted to produce a first electrical signal consisting of a major component which is dependent upon sound produced by the desired first source and a minor component dependent on the sound produced by the undesired second source a second microphone positioned adjacent the second source and adapted to produce a second electrical signal dependent primarily upon the sound produced by said second source; and means for comparing said first and second electrical signals in such proportions as to produce a resultant control signal which varies substantially with the sound produced by said first desired source and which is substantially independent of the sound produced by said second undesired source.

2. Apparatus for producing an electrical control signal which varies in accordance with noise produced by a material reduction mill, said mill being so situated that the noise produced by the material reduction mill becomes mixed with extraneous noise, said apparatus comprising; a first microphone positioned adjacent said material reduction mill and adapted to produce a first electrical signal consisting of a major component which is dependent upon the sound produced by the material reduction mill and a minor component dependent on the extraneous noise, a second microphone positioned and adapted to produce a second electrical signal dependent for the most part on said extraneous noise, and means for comparing the first and second electrical signals in such proportion to produce a resultant control signal which varies in accordance with the noise, produced by said material reduction mill and which is substantially independent of said extraneous noise.

3. Apparatus as defined in claim 2 in whichthe extraneous noise to which the second microphone is subjected is grinding noise from a mill adjacent to the mill with which said apparatus is associated.

4. Apparatus as defined in claim 3, in which at least one sound barrier is arranged between the two mills to aid in making the first electrical signal dependent primanly on the direct grinding noise from the mill to be controlled and in making the second electrical signal dependent primarily on the grinding noise from the adjacent mill.

5. Apparatus as defined in claim 1 in which the means 7 for combining the first and second electrical signals comprises an amplifier for each of said signals adapted to producea direct current output voltage, a direct current bridge circuit adapted to subtract the direct current output voltage derived from the second electrical signal from the direct current output voltage derived from the first electrical signal thereby producing a resultant control signal which varies in accordance with said sound produced by a desired first source and which is substantially independent of the sound produced by the second undesired source.

6. Apparatus as defined in claim 1 in which the means for combining the first and second electrical signals comprises an amplifier for each of said signals adapted to amplify a predetermined pass band of frequencies and to produce a direct current output voltage, a direct current bridge circuitvadapted to subtract the direct current output voltage derived from the second electrical signal from the direct current output voltage derived from the first electrical signal thereby producing a resultant control signal which varies in accordance with the sound produced by said first desired source and which is substantially independent of the sound produced by the second undesired source, and integration means adapted to average rapid fluctuations in said resultant control signal.

7. Apparatus as defined in claim 2, in which the means for combining the first and second electrical signals comprises an amplifier for each of said signals adapted to produce a direct current output voltage, a direct current bridge circuit adapted to subtract the direct current output voltage derived from the second electrical signal from the direct current output voltage derived from the first electrical signal thereby producing a resultant control signal which varies in accordance with said noise produced by said material reduction mill and which is sub stantially independent of said extraneous noise.

8. Apparatus as defined in claim 3, in which the means for combining the first and second electrical signals comprises an amplifier for each of said signals adapted'to produce a direct current output voltage, a direct current bridge circuit adapted to subtract the direct current output voltage derived from the second electrical signal from the direct current output voltage derived from the first electrical signal thereby producing a resultant control signal which varies-in accordance with said noise produced by said material-reduction mill and which is substantially independent of said extraneous noise.

9. Apparatus as defined in claim 2 in which the means for combining the first and second electrical signals comprises an amplifier for each of said signals adapted to amplify a predetermined pass band of frequencies and to produce a direct current output voltage, a direct current bridge circuit adapted to subtract the direct current output voltage derived from the second electrical signal from the direct current output voltage derived from the first electrical signal thereby producing a resultant con- .trol signal which varies in accordance with the noise produced by said material production mill and which is substantially independent of the extraneous noise, and integration means adapted to average rapid fluctuations in said resultant control signal.

10. Apparatus as defined in claim 3, in which the means for combining the first and second electrical signals comprises an amplifier for each of said signals adapted to amplify a predetermined pass band of frequencies and to produce a direct current output voltage, a direct current bridge circuit adapted to subtract the direct current output voltage derived from the second electrical signal from the direct current output voltage derived from the first electrical signalvthereby producing a resultant control signal which varies in accordance with the noise produced by said material production mill and which is substantially independent of the extraneous noise, and integration means adapted to average rapid fluctuations in said resultant control signal.

Reicrcnces Cited in the file of this patent UNITED STATES PATENTS 2,338,551 Stanko Ian. 4, 1944 2,350,010 Beekley May 30, 1944 2,611,035 Duncan Sept. 16, 1952 

